In the seas above the Arctic circle lives the narwhal, the ‘unicorn of the sea’. Narwhals are unique in that they have a swordlike, spiral tusk that grows right through their upper lip. Swimming in groups of hundreds of individuals, these unique mammals dive to extreme depths under the arctic ice.
Found primarily in Canadian Arctic and Greenlandic waters rarely south of 65°N latitude, the narwhal is a specialized arctic predator that feeds mainly on fish, shrimp and squid. In the winter, they hunt for prey under the dense pack ice where they can only surface in narrow fissures. The narwhals make some of the deepest dives of all marine mammals, going to depths of up to 1800m. Unbelievably, by some special adaptations they can carry enough oxygen to enable them to spend more than 3 hours a day below 800 meters; a depth where the pressure is enormous and life exists in complete darkness.
The most characteristic feature of the Narwhal is its huge tusk. Measuring an incredible two to three meters long, the male Narwhal’s tusk is actually a tooth, similar like elephants have. The most widely accepted theory for the role of this large tooth is that it is a sexual trait, much like the antlers of a male deer or the feathers of a peacock. Males use their tooth to compete with eachother for females and may help determine social rank. The sexual selection theory was originally put forward by Charles Darwin in his book The Descent of Man, and Selection in Relation to Sex (1871). Darwin makes a good case:
When the males are provided with weapons which the females do not possess, there can hardly be a doubt that they … have been acquired through sexual selection.
Recent research found evidence that the tusk may furthermore be an important sensory organ to gather valuable information for survival in the arctic waters, since its contains an incredible 10 million nerve endings. Researchers say this enables the narwhal to detect all sorts of information such as temperature, pressure, motion, and the salt contents of the water. Although narwhals mainly use their vocal skills for navigation, sensing prey, and communication, the tusk is expected to share some of these functions.
Narwhals have gotten their name from the the old Norse word for corpse ‘nar’, referencing to the animals pale colour and mottled skin. While populations appear stable with a world population of some 75000 individuals, the narwhal has been deemed particularly vulnerable to climate change due to a narrow geographical range and specialized diet.